QT Interval: How to Measure It and What Is "Normal"

Ilan Goldenberg, M.D.; Arthur J. Moss, M.D.; Wojciech Zareba, M.D., Ph.D.


J Cardiovasc Electrophysiol. 2006;17(3):333-336. 

In This Article

Heart Rate Correction in Patients with Sinus Arrhythmias

If a stable sinus rhythm cannot be obtained in a patient, more advanced methods evaluating repolarization dynamicity may be required. The QT interval adapts to heart rate changes with a delay known as QT hysteresis or QT lag. When the change in the heart rate persists for several minutes, the QT lag is visible on the trend of QT and RR intervals. The QT adapts more slowly to decelerations than to accelerations of the heart rate. The plot of QT versus RR intervals during dynamic adaptation of repolarization to heart rate changes forms a loop known as hysteresis. QT-RR hysteresis pattern is highly individual and, therefore, methods that take into account individual profiles are required.